For a perfectly competitive industry with identical firms, the long-run industry supply curve is: perfectly elastic. horizontal. based on minimum average costs. All of these are characteristics of the long-run supply curve.

All of these are characteristics of the long-run supply curve.

Explanation:

In the long run supply curve shape is dependent on wether the industry is a constant cost industry, a decreasing cost industry, or an increasing cost industry. It can be horizontal, upward sloping, or downward sloping.

In constant cost market price remains constant with increasing output. Supply curve is horizontal.

In decreasing cost industry supply curve is sloping downward and cost reduces with output.

In increasing cost industry supply curve is upward sloping and cost increases with increased output.